Generally, a crawler belt provided for a work vehicle of this type encircles an idler tumbler (idler) and a driving wheel (sprocket), forming an elliptical shape to provide an endless track between these idler tumbler and driving wheel. The driving wheel is rotatively driven to cause the crawler belt to rotate about a path between the idler tumbler and the driving wheel so that the work vehicle is stably propelled over the irregular terrain or the like.
The crawler belt is composed of a track chain in which a plurality of regular links are rotatably connected to each other at their ends; track shoes attached to the regular links respectively; and a coupling device for connecting the opposed ends of the track chain to form the crawler belt into a loop.
In the track chain of this crawler belt, the ends of every adjacent regular links are made to overlap each other and connected in belt-like form with the aid of coupling pins called “regular pins”. The allowance for clamping the regular pins relative to the regular links is set to a relatively small value so that the regular pins cannot be easily removed from and inserted into their associated regular links.
At the position where the leading and trailing ends of the belt-like track chain of the crawler belt are connected together or the track chain of the crawler belt, which has been connected into a loop, is disconnected, a master link for connection/disconnection, a master pin or both of them are disposed as the coupling device. In one known connection configuration which employs both a master link and a master pin, the master link and a regular link are coupled by a coupling pin called “master pin”, forming an endless crawler belt. In this configuration, the allowance for clamping the master pin relative to the master link is set to a relatively great value, and therefore, the master pin can be removed or inserted by use of a press machine.
For performing maintenance on the crawler belt, removal of the crawler belt from the idler tumbler and the driving wheel and/or mounting of the crawler belt so as to encircle the idler tumbler and the driving wheel is sometimes performed.
In this case, the removal of the crawler belt is performed in the following way. Specifically, the master link and the regular link are disconnected from each other by taking the master pin out. Then, the crawler belt wound around the idler tumbler and the driving wheel is linearly stretched.
On the other hand, the mounting of the crawler belt is performed as follows. Specifically, the linearly-stretched crawler belt is wound around the idler tumbler and the driving wheel. Then, the master pin is inserted into the master link and the regular link thereby to connect them.
By inserting and removing the master pin in this way, the crawler belt can be mounted and dismounted.
However, the removal and insertion of the master pin requires a press machine and involves a lot of trouble, which causes difficulties in mounting and dismounting of the crawler belt.
One known technique for solving the above problem does not use a master pin but uses a splittable master link. More specifically, this master link is constituted by two half links and set up by fastening these two half links to each other with a track shoe mounting bolt.
The two-splittable link described herein includes a convex part and a concave part which are brought into engagement with each other upon set-up. One of the two half links is connected to the other end of a regular link adjacent to one end of the master link whereas the other half link is connected to one end of a regular link adjacent to the other end of the master link.
The convex part and the concave part of the two half links are thus engaged and the two half links are fastened by the track shoe mounting bolt whereby the crawler belt can be connected in endless form. Reversely, the crawler belt can be disconnected by loosening and removing the track shoe mounting bolt and disengaging the convex part and concave part of the two half links from each other.
The method utilizing a splittable master link can more easily accomplish mounting and dismounting of the crawler belt, compared to the method that uses a master pin and the method that uses both a master pin and a master link.
However, the convex part and the concave part have to be tightly engaged with each other in order to firmly combine the two half links, which constitute the master link, by tightening the track shoe mounting bolt. This raises the need for special equipment capable of machining the convex and concave parts with high accuracy in the manufacture of the two half links. As a result, there arises the problem that the production cost of the master link increases.
In addition, since the master link is configured to be set up by tightly fastening the two half links with the track shoe mounting bolt, there is a risk that the track shoe mounting bolt fractures, for example, when an impactive load is imposed on the master link.
As one attempt for solving the above problem, the master link disclosed in Patent Literature 1 has been proposed.